Re: [PATCH v7 3/7] KVM: VMX: Pass through CET related MSRs to Guest

Yang Weijiang
2019-10-18T01:28:09Z

On Thu, Oct 17, 2019 at 01:04:11PM -0700, Sean Christopherson wrote:
> On Wed, Oct 09, 2019 at 02:15:09PM +0800, Yang Weijiang wrote:
> > On Wed, Oct 02, 2019 at 11:18:32AM -0700, Jim Mattson wrote:
> > > > + kvm_xss = kvm_supported_xss();
> > > > + cet_en = guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> > > > + guest_cpuid_has(vcpu, X86_FEATURE_IBT);
> > > > + /*
> > > > + * U_CET is a must for USER CET, per CET spec., U_CET and PL3_SPP are
> > > > + * a bundle for USER CET xsaves.
> > > > + */
> > > > + if (cet_en && (kvm_xss & XFEATURE_MASK_CET_USER)) {
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
> > > > + }
> > >
> > > Since this is called from vmx_cpuid_update, what happens if cet_en was
> > > previously true and now it's false?
> > >
> > Yes, it's likely, but guest CPUID usually is fixed before
> > guest is launched, do you have any suggestion?
>
> Re-enable interception. kvm_x86_ops->cpuid_update() is only called in
> the ioctl flow, i.e. it's not performance critical.
>
OK, will add a *else* clause to re-intercept the MSRs as Jim suggested.

> > > > + /*
> > > > + * S_CET is a must for KERNEL CET, PL0_SSP ... PL2_SSP are a bundle
> > > > + * for CET KERNEL xsaves.
> > > > + */
> > > > + if (cet_en && (kvm_xss & XFEATURE_MASK_CET_KERNEL)) {
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW);
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW);
> > > > +
> > > > + /* SSP_TAB only available for KERNEL SHSTK.*/
> > > > + if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> > > > + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB,
> > > > + MSR_TYPE_RW);
> > > > + }
> > > > +}
> > > > +
> > > > static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> > > > {
> > > > struct vcpu_vmx *vmx = to_vmx(vcpu);
> > > > @@ -7025,6 +7062,8 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> > > > if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
> > > > guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
> > > > update_intel_pt_cfg(vcpu);
> > > > +
> > > > + vmx_intercept_cet_msrs(vcpu);
> > > > }
> > > >
> > > > static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> > > > --
> > > > 2.17.2
> > > >